An outdoor unit of an air conditioner includes: an outdoor heat exchanger exchanging heat between outdoor air and a refrigerant; an outdoor fan sending the outdoor air to the outdoor heat exchanger; and a fan motor acting as a drive source of the outdoor fan. Since the outdoor unit is placed outside, the outdoor fan in a stopped state could rotate by an influence of, for example, wind. Moreover, immediately after stopping the operation, the outdoor fan keeps rotating for a while due to moment of inertia. When the outdoor fan is activated under these circumstances, the fan motor could be intentionally left undriven, depending on a rotation speed of the outdoor fan, because sufficient outdoor air is sent to the outdoor heat exchanger. Thus, it is desirable to know a state of the outdoor fan before its activation.
Patent Document 1 discloses a technic which involves detecting an induced voltage of a fan motor before activation, and determining an activation sequence of the fan motor based on the result of the detection.